From Ryzom Wiki

All tribes of Atys have some idealogical purpose, are aligned to one of the Higher Powers, have a number of mission givers on their payroll, and only attack those who have low fame with them. (Even if for some tribes, their purpose is 'burn and pillage', and those who have low fame with them is almost everyone.)

Bandit groups are different, they are homins who have no other purpose than to lie in wait in the wilderness and ambush any traveller who comes near. There is no befriending them or talking to them. Any homin who comes too close to their camp will always be attacked.

For new players, a good way to distinguish bandits from tribes is to look at their titles: If the NPCs have a title identical to their name, they are bandits.